Data on deltamethrin resistance in Oropsylla hirsuta fleas from black-tailed prairie dogs in Conata Basin, Buffalo Gap National Grassland and Badlands National Park, South Dakota, 2014-2015. Two data files are available, one from "Mortality trials" and another from "recovery trials". The data from "Mortality trials" includes information on bioassays in which fleas were subjected to deltamethrin in Petri dishes. In 2014, fleas were collected from colonies of black-tailed prairie dogs that had been treated with a deltamethrin-containing dust since 2005 (Dusted) and colonies that had never been treated with deltamethrin (Not Dusted). The fleas were placed in Petri dishes with deltamethrin. All fleas were alive at the start of these trials. The fleas were assessed for mortality every 5 minutes until all fleas appeared dead (i.e., for 55 minutes). The data includes the treatment category for each line of data (fleas from Dusted or Not Dusted colonies); the minute marks for assays (0 through 55 minutes); and the numbers of fleas alive during each minute mark. The data from "Recovery trials" includes information on bioassays in which fleas were assessed for recovery after deltamethrin treatment. After the mortality trials (described above), all fleas appeared dead. Fleas were then placed in clean vials or Petri dishes and assessed for recovery 40 hours later (i.e., assessed for an ability to actually survive and recover from deltamethrin treatment). The data (2014 and 2015 separately) includes the years of sampling; the treatment category for each line of data (fleas from Dusted or Not Dusted colonies); the numbers of fleas that recovered (i.e., were resistant to deltamethrin); and the numbers of fleas that were actually dead. Individual study sites are occupied by species of conservation concern, including endangered black-footed ferrets. Thus, the data are linked to the general study area, Conata Basin, South Dakota. Funding and logistical support were provided by US Geological Survey, US Forest Service, National Park Service, US Fish and Wildlife Service, Colorado State University, the Centers for Disease Control and Prevention, Prairie Wildlife Research, National Fish and Wildlife Foundation, and World Wildlife Fund. This research was supported by Grant-Cooperative Agreement Number G14AC00403 from the US Geological Survey.